Sensitometer apparatus

ABSTRACT

A sensitometer having a replaceable integral exposure source unit including both a constant source of actinic energy and an energy modulator. Because of the fixed relationship between its individual components, the modulated energy output remains at a known, constant level over the life of the exposure unit.

United States Patent 1 Sanford [451 Oct. 17, 1972 [54] SENSITOMETERAPPARATUS 2,053,317 9/1936 Billing ..355/71 [72] Inventor: Lloyd C.Sanford, Acton, Mass.

Primary ExaminerJohn M. Horan 1 Assign: ltek l Lexington Mass-Attorney-Homer 0. Blair, Robert L. Nathans, Lester 22 i April 1 19 S.Grodberg and John E. Toupal pp 717,870 57 ABSTRACT A sensitometer havinga replaceable integral exposure 1 1 6/ 9/ source unit including both aconstant source of actinic 1 3 Cl 1 1/40, energy and an energymodulator. Because of the fixed 1 Field 0f Search 356/229, relationshipbetween its individual components, the

356/235 modulated energy output remains at a known, constant level overthe life of the exposure unit. [56] References Cited 13 Claims, 4Drawing Figures UNITED STATES PATENTS Twymanw, ..355/7l X SENSITOMETERAPPARATUS BACKGROUND OF THE INVENTION This invention relates tosensitometry. More precisely, the invention disclosed herein relates toapparatus useful for evaluating the response of photographic film toactinic energy which in turn is indicative of such properties as thephotographic speed, density production, the contrast, processingcharacteristics, and the like of photographic film material.

Sensitometry is well known to those skilled in the photographic art andessentially involves the measurement and evaluation of the response ofphotographic materials to radiant energy. As presently practiced,sensitometry involves the .determination of the density of photographicfilm materials exposed to a source of illumination of known intensityand spectral distribu tion for a known time, the development of theexposed film under precisely controlled and reproducible conditions, thecorrelation of the densities measured in the film to establishedstandards for density, and the interpretation of the results.

The present invention relates to a novel sensitometer having acombination of structural elements which cooperate in an integratedfashion to permit the activation of a photosensitive material with anexposure source having a known and constant luminous flux output.Sensitometers heretofore used in the field consist of a light source anda means of varying the exposure given to the film by varying either theintensity and/or the time of that exposure. Light sources forsensitometric exposures must be selected with consideration to boththeir suitability for the sensitive material as well as theirsuitability in intensity and spectral distribution. Moreover,precautions must be taken so that the total illumination by the lightsource incident upon the film is maintained constant together with thespectral distribution so that valid interpretations may be made.

In some instances heretofore, sensitometers have employed incandescentsources such as tungsten-filament lamps. Generally in suchsensitometers, the light has passed from the incandescent source to thefilm through a calibrated shutter for controlling the exposure interval.However, an outstanding problem in such sensitometers is that it isextremely difficult to control both the intensity of light obtained fromincandescent sources as well as the spectral distribution thereof. Forexample, transient variations in voltage produce very great changes notonly in the quantity or intensity of the incandescent light but also inthe color or spectral distribution thereof. Accordingly, sensitometricdeterminations made from such sensitometers are usually unreliableunless precautions are taken to assure that the intensity and thespectral distribution of the illumination of the source can beaccurately reproduced from time to time.

In order to avoid the disadvantages implicit in the use of incandescentsources, various sensitometers have been proposed which utilize flashlamps. Since the light output intensity of these lamps varies only asthe square of applied voltage, transient voltage variations during theproduction of very short light flashs do not materially alter lightoutput. In addition, the spectral distribution of the produced light isnearly independent of voltage.

Although substantially alleviating problems associated with non-uniformlight sources, flash lamp sensitometers have not solved fully theburdensome requirements for frequent instrument calibration. Precisionphotographic sensitometry requires accurate calibration of exposurelevels which are determined not only by lamp output intensity but alsoby the elements normally used to modulate that output. Since eachcomponent in an exposure source possesses unique opticalcharacteristics, any change in their combination will modify exposureoutput levels regardless of the components individual consistency. Thus,for example, replacement of either the flash lamp or density wedge in atypical exposure source will shift previous log exposure plot points onthe X-axis of a conventional sensitometric plot. Accordingly, aninstrument must be recalibrated and a new sensitometric plot preparedafter each component change in its exposure source. Not only are theserequirements burdensome but since individual exposure source componentsand particularly density wedges are readily exchanged in conventionalsensitometers, a user of a particular instrument is not always assuredthat an available sensitometric plot corresponds to a current set ofexposure components. Consequently, he must either risk inaccuratemeasurements or recalibrate the exposure source.

The object of this invention, therefore, is to provide an improvedsensitometer that improves accuracy while reducing calibrationrequirements.

CHARACTERIZATION OF THE INVENTION The invention is characterized by theprovision of a sensitometer including an integral exposure source unitremovably mounted within a light-tight housing. The exposure unit isformed by a light source retained in an enclosure having an apertureportion formed by a light modulator that receives light from the lightsource and provides a variably modulated output thereof. Attached to thelight-tight housing is a retainer adapted to fix photosensitivematerials in position to receive modulated light from the apertureportion of the enclosure. By providing all required components of anexposure source in an integral replaceable unit, uniform exposure outputlevels are insured for the useful life of the unit. Therefore, only onegraduated sensitometric plotting sheet need be prepared for eachexposure source unit.

One feature of this invention is the provision of a sensitometer of theabove type wherein the light source comprises a plurality of electricflash lamps and the light modulator is a photographic density wedge. Theflash lamps provide a highly desirable, uniform source of luminous fluxand the density wedge renders the instrument suitable for a wide varietyof measurement applications.

Another feature of this invention is the provision of a sensitometer ofthe above featured type wherein the exposure source enclosure comprisesa block of light transmissive material potted around the electric flashlamps. The enclosure block provides the exposure unit with a high degreeof physical stability and resultant exposure output level consistency.

Another feature of the invention is the provision of a sensitometer ofthe above featured type wherein the exposure unit enclosure is arectangular block with one surface forming the aperture portion andpolished specular remaining surfaces adapted to reflect light receivedfrom the flash lamps toward the aperture portion. By providing specularsurfaces, the exposure source enclosure functions as a light directorand mixer tEat intensifies the luminous flux received by the apertureportion.

Another feature of this invention is the provision of a sensitometer ofthe above featured types wherein the flash lamps are embedded adjacent aspecular, reflectively coated enclosure block and surface opposite thesurface forming the aperture portion. In this arrangement, thefrustrated internal reflection within the enclosure block creates amultiplicity of virtual light sources behind the aperture portionthereby providing extremely uniform illumination thereof.

These and other objects and features of the present invention willbecome more apparent upon a perusal of the following specification takenin conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic, partially broken away, side view of a preferredsensitometer embodiment of the invention;

FIG. 2 is a front view of the exposure source unit shown in FIG. 1;

FIG. 3 is a top view of the exposure source unit shown in FIG. 2; and

FIG. 4 is a bottom view of the exposure source unit shown in FIGS. 2 and3.

Referring now to FIG. 1 there is shown the sensitometer 11 including thecover 12 pivotally attached to the light-tight housing 13. Secured tothe bottom of the cover 12 is the light seal member 14 formed, forexample, of a suitable foam rubber material. Upon closure of the cover12, the seal member 14 contacts the top surface 15 of the light-tighthousing 13 thereby light-sealing the opening 16 disposed therein. Asshown in the broken away portion of FIG. 1, the integral exposure sourceunit 17 is positioned within the light-tight housing 13. Secured withinthe housing 13 are the mounting brackets 18 that align the exposuresource unit 17 with the opening 16. The bottom plate 19 is attached bythe hinge 21 to permit opening of the lighttight housing 13 and removalof the source unit 17.

As shown in FIGS. 2-4, the source unit 17 comprises the solidrectangular block 22 made of a suitable light transmissive material suchas plastic or glass. Forming the top surface of the exposure unit 17 isthe light modulator plate 23 which is permanently fixed to therectangular block 22 by, for example, a suitable cement. The lightmodulator plate 23 possesses the longitudinally disposed opaque marginalregions 24 that straddle the conventional photographic density wedge 25.

Located within the block 22 adjacent the end 26 opposite the densitywedge 25 are the actinic energy sources 27 which are preferably flashlamps of, for example, the tungsten or xenon type. Although three lamps27 are shown, it will be appreciated that either a single lamp or othernumbers oflamps can be used. The lamps 27 can be embedded within theblock 22 in any suitable manner as, for example, by being potted thereinor by being inserted and sealed within bored holes. All surfaces of theunit 17 are polished, specular surfaces except the end surface formed bythe light modulator plate 23. The opposite end 26 adjacent the lamps 27is coated with a layer 29 of a light reflective substance such asaluminum.

During operation of the sensitometer 11, a film (not shown) to beexposed is placed over the exposure window 16 with its photosensitivecoating facing the exposure unit 17. The cover 12 is closed against thesurface 15 causing the seal member 14 to form a light-tight seal andpress the inserted film into intimate contact with the exposure window.Then, a firing switch (not shown) is actuated causing a power supplycircuit (not shown) within the light-tight housing 13 to energize theflash lamps 27. The illumination produced by energization of the flashlamps 27 is directed by the exposure source block 22 toward the exposureaperture formed by the density wedge 25. After being variably modulatedby passage through the density wedge 25, this illumination exposes theretained film in the conventional manner. The details of the powersupply circuit utilized to energize the lamps 27 does not, per se, forma portion of this invention. However, power supplies suitable for use inthe invention are disclosed in U. S. Pat. No. 3,001,459 issued Sept. 26,1961 and in U. S. Pat. Application Ser. No. 560,557 entitled ImprovedSensitometer and filed June 27, 1966 by the present applicant.

Because all components of the exposure source 17 are formed into anintegral unit, the modulated exposure output levels from the densitywedge 25 remain constant over the life of the flash lamps 17. Therefore,a single calibrated sensitometric plotting sheet of the conventionaltype will provide accurate log exposure plot points for the life of theexposure unit 17. In practice, this graduated plotting sheet would besupplied to the user by the manufacturer along with the associatedexposure unit 17. After the absolute luminous flux density output of thelamps 27 has been modified by extended use, the user of the sensitometer11 merely opens the bottom 19 and replaces the entire exposure unit 17with a replacement unit. Thereafter, precision photographic sensitometryagain is obtained by utilizing a new sensitometric plotting sheetcorresponding uniquely to the replacement unit.

Additional measurement accuracy is provided by the opticalcharacteristics of the rectangular block 22. The specular surfaces 28and 29 transmit the light emanating from the flash lamps 27 toward theoutput aperture formed by the density wedge 25. However, because of thefrustrated internal reflection produced by these surfaces, amultiplicity of virtual light source are created behind the aperture 25.Therefore, the aperture 25 is illuminated extremely uniformly andmeasurement accuracy of the sensitometer 11 is enhanced.

In the invention embodiment shown and disclosed, a flash'lamp source ofactinic energy is used to provide the constant exposure time requiredfor measurement accuracy. It will be obvious, however, that other typesof constant exposure mechanisms could be used within the scope of theinvention. For example, a conventional unit comprising a continuouslight source and an accurately timed shutter could be used to supply theconstant exposure.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims the inventioncan be practiced otherwise than as specifically described.

What is claimed is:

I. In a sensitometer which enables the determination of the responsecharacteristics of a photosensitive medium to actinic radiation byexposing the photosensitive medium to actinic radiation, from an actinicenergy source means, which has been modulated by a variable densityenergy modulation means, the improvement comprising: an exposure sourceunit including said actinic energy source means, said variable densityenergy modulation means, and means for providing a plurality ofradiation paths from said actinic energy source means to said energymodulation means, said exposure source means to said energy modulationmeans, said exposure source unit comprising a unitary,integrally-constructed unit for preventing said actinic energy sourcemeans or said energy modulation means from being replaced without theeffective destruction of the exposure source unit, and including:

a. means to irreplaceably secure said actinic energy source means tosaid integrally-constructed exposure source unit of said sensitometerfor preventing the replacement of said actinic energy source meanswithout breaking the exposure source unit;

and

. means to irreplaceably secure said energy modulation means to saidintegrally-constructed exposure source unit of said sensitometer forpreventing the replacement of said energy modulation means withoutbreaking the exposure source unit.

2. A sensitometer apparatus according to claim 1 wherein said actinicenergy source means comprises an electric flash lamp.

3. A sensitometer apparatus according to claim 1 wherein said exposuresource unit includes a block of actinic energy transmissive materialpotted around said actinic energy source means.

4. A sensitometer apparatus according to claim 1 wherein said energymodulation means comprises a photographic density wedge.

5. A sensitometer apparatus according to claim 4 wherein said actinicenergy source means comprises an electric flash lamp.

6. A sensitometer apparatus according to claim 5 wherein said exposuresource unit includes a rectangular block of light transmissive materialpotted around said flash lamp.

7. A sensitometer apparatus according to claim 6 wherein said densitywedge is located along one elongated surface of said block and theremaining surfaces are polished, specular surfaces adapted to reflectlight received from said flash lamp toward said density wedge.

8. A sensitometer apparatus according to claim 7 wherein said flash lampis potted within said block adjacent an end surface thereof oppositesaid aperture portion.

9. A sensitometer according to claim 8 wherein said end surface of saidblock is coated with a reflective substance.

10. A sensitometer apparatus according to claim 1 wherein said exposuresource unit includes a rectangular block of actinic energy transmissivematerial potted around said actinic energy source means.

11. A sensitometer apparatus according to claim 10 wherein said energymodulation means is located along on elon ated su cc of said block andthe remainin sur faces are polis l ied, specular surfaces adapted kreflect energy received from said energy source means toward said energymodulation means.

12. A sensitometer apparatus according to claim 11 wherein said energysource means is potted within said block adjacent an end surface thereofopposite said aperture portion.

13. A sensitometer according to claim 12 wherein said end surface ofsaid block is coated with a reflective substance.

1. In a sensitometer which enables the determination of the responsecharacteristics of a photosensitive medium to actinic radiation byexposing the photosensitive medium to actinic radiation, from an actinicenergy source means, which has been modulated by a variable densityenergy modulation means, the improvement comprising: an exposure sourceunit including said actinic energy source means, said variable densityenergy modulation means, and means for providing a plurality ofradiation paths from said actinic energy source means to said energymodulation means, said exposure source unit comprising a unitary,integrally-constructed unit for preventing said actinic energy sourcemeans or said energy modulation means from being replaced without theeffective destruction of the exposure source unit, and including: a.means to irreplaceably secure said actinic energy source means to saidintegrally-constructed exposure source unit of said sensitometer forpreventing the replacement of said actinic energy source means withoutbreaking the exposure source unit; and b. means to irreplaceably securesaid energy modulation means to said integrally-constructed exposuresource unit of said sensitometer for preventing the replacement of saidenergy modulation means without breaking the exposure source unit.
 2. Asensitometer apparatus according to claim 1 wherein said actinic energysource means comprises an electric flash lamp.
 3. A sensitometerapparatus according to claim 1 wherein said exposure source unitincludes a block of actinic energy transmissive material potted aroundsaid actinic energy source means.
 4. A sensitometer apparatus accordingto claim 1 wherein said energy modulation means comprises a photographicdensity weDge.
 5. A sensitometer apparatus according to claim 4 whereinsaid actinic energy source means comprises an electric flash lamp.
 6. Asensitometer apparatus according to claim 5 wherein said exposure sourceunit includes a rectangular block of light transmissive material pottedaround said flash lamp.
 7. A sensitometer apparatus according to claim 6wherein said density wedge is located along one elongated surface ofsaid block and the remaining surfaces are polished, specular surfacesadapted to reflect light received from said flash lamp toward saiddensity wedge.
 8. A sensitometer apparatus according to claim 7 whereinsaid flash lamp is potted within said block adjacent an end surfacethereof opposite said aperture portion.
 9. A sensitometer according toclaim 8 wherein said end surface of said block is coated with areflective substance.
 10. A sensitometer apparatus according to claim 1wherein said exposure source unit includes a rectangular block ofactinic energy transmissive material potted around said actinic energysource means.
 11. A sensitometer apparatus according to claim 10 whereinsaid energy modulation means is located along one elongated surface ofsaid block and the remaining surfaces are polished, specular surfacesadapted to reflect energy received from said energy source means towardsaid energy modulation means.
 12. A sensitometer apparatus according toclaim 11 wherein said energy source means is potted within said blockadjacent an end surface thereof opposite said aperture portion.
 13. Asensitometer according to claim 12 wherein said end surface of saidblock is coated with a reflective substance.